Reflecting on solar PV fire risk

Government figures confirm that the use of solar PV to generate electricity in the UK has grown rapidly since 2010, increasing capacity from 95 MW to 13,800 MW at the end of 2021. There are now over one million solar PV installations in the UK. In 2021 solar PV contributed more than ten per cent of renewable generation and more than four per cent of total electricity generation in the UK. ¹

With rising energy prices, interest in solar PV installations is on the up ², especially as householders emerge from fixed rate energy deals to the shock of record-breaking energy price increases.

The Rules Governing Solar PV Safety

NBS (National Building Specification), a UK-based business providing construction specification information for architects, engineers and other building professionals to describe the materials, standards and workmanship of a construction project gives a detailed overview of the current safety requirements. ³

There are several standards that PV products should comply with (BS EN 61730-1, BS EN 61215, BS EN 61646, MCS 0065), which include (amongst other factors) requirements that address fire hazards. The Microgeneration Certification Scheme (MCS) provides building owners with a measure of confidence in the installers and products used. Furthermore, PV systems that form part of the roof structure should satisfy a fire exposure test, eg DD CEN/TS 1187 test 4 or BS 476-3. This test seeks to ensure that fire will not spread between buildings via the roofs.

The Risks Related to Solar Panels

Notwithstanding these regimes for installers and products, there is currently no national UK guidance specific to fighting fires involving PV systems, despite PV systems presenting new risks to firefighters, especially from the risk of electric shock and electrocution. However, the BRE National Solar Centre has carried out some in-depth analysis of the causes and challenges of solar PV fires as uncovered by previous incidents in the UK. ⁴

Jim Foran, who has pioneered award winning solar PV safety solutions in Australia and the UK ⁵ and demonstrated their use at previous IFE international conferences, explains: “Once solar panels are up, they don’t make any noise, they are out of out of sight and out of mind. When it comes to causes of fires in solar panels it can be something as simple as a branch falling on the roof that then cracks the panels. Those cracks become hotspots which then become arcs, which then become fires. It can be vermin, rats and birds pulling or chewing at the wiring. But globally, poor installation or poor-quality componentry is the biggest factor. For example, in Australia around one in five installations inspected has issues. ⁶”

The reality firefighters face is that if solar panels are exposed to light, they will continue to produce potentially lethal amounts of direct current (DC) electricity, even if elsewhere in the building the electricity has been isolated. In practice, this means anyone operating near a solar panel system during daylight hours is effectively engaging with live electrical equipment.
Parts of the system are always live while light falls on the panels, even artificial lighting may generate small currents. The only way to stop the PV panels generating electricity even after they have been isolated is to block out the light. In the US portable covers are being trialled, while in the UK London Fire Brigade has successfully trialled a black liquid polymer film that is discharged from a standard nine-litre cylinder, or fire extinguisher, which can be used to seal the units to stop them generating energy from sunlight. ⁷

Beyond the panels themselves, if the structure is metal or steel frame, then an accidental short may result in parts of the building being ‘live’. There is the added risk of electric shock if cables are cut or become damaged by fire. This includes cables from battery banks where these are used to store generated electricity.

A Wide Range of Firefighting Issues

The NBS points out that firefighters may not immediately recognise they are dealing with a PV system, especially as there are many different types of systems available and, in commercial buildings, these may be hidden on flat roofs. The new MCS installation guide (MCS, 2012) requires that a firefighter’s label be affixed in a prominent place close to the electrical shut-off point.

Should the roof of the building be affected by fire, then the additional mechanical loading due to the weight of PV panels, or additional wind-loading caused by the panels, may cause early collapse of the roof.

The NBS also highlights the additional risks of solar arrays that are stood off from the roof which may cause a channelling effect, thus exacerbating a fire affecting the roof. There is also the risk that panels, or glass from the panels, may break and fall onto personnel below.

Toxic Problem

Another potential risk to firefighters is the properties of the panels themselves. Sandwiched between the protective glass, frame and back sheet of the solar panel, solar cells present no risk to health, but once a panel burns and the

solar cells are exposed, the burning panels can be highly toxic and dangerous to humans. Solar cells vary in makeup, some contain the carcinogens cadmium telluride and gallium arsenide, as well as the potentially lethal phosphorous, so precautions are essential.

Inhalation of these toxic nanoparticles cause silicosis of the lungs and should be treated with the same precautions as asbestos. Self-contained breathing apparatus (SCBA) should always be utilised in incidents involving burning solar panels.

Battery Storage

Increasingly, solar PV installations are both connected to the grid so that building owners can earn feed in tariffs if they export their excess energy or being installed with the option of battery storage where this excess energy can be stored in the building for future use.

They will be mounted within garages next to normal household possessions, next to parked cars many of which will have similar battery storage systems as well. They will not always be easily accessible and the risks of lithium-ion batteries from a fire safety perspective, especially have been well-documented.

The implications of on-site solar PV generation for fire and emergency services personnel are significant and as part of its sustainability strategy, the IFE is building the knowledge base of fire safety challenges arising from new technologies and materials driven by sustainability to enable global knowledge sharing and development of best practice.

To find out more visit: www.ife.org.uk